Multi-chip arrays are used in many image-related applications, for example, for scanning, copying, or printing operations. As an example, photosensor chips for scanning document images can be placed in a row to form a linear array. Suitable supporting circuitry for the array is integrated onto a silicon chip. A typical architecture for such an array is given, for example, in commonly-owned U.S. Pat. No. 5,153,421.
High precision, low damage dicing or scribing is needed on the ends of chips that are used in linear multi-chip arrays in which the chips are “butted” or placed end-to-end to maintain a desired spacing between the chips. For example, for butted photosensor chips, if sensors on the chips are spaced “x” amount apart, the desired spacing between two butted chips is such that the respective sensors closest to the butted ends are spaced “x” amount from each other to maintain the sensor spacing on the chips. That is, the on-chip sensor spacing is preserved across the joint of the butted chips.
FIG. 7 is a representation of a prior art method of dicing a wafer. The prior art teaches the use of a mechanical blade to dice a wafer to form chips, or dies. For example, commonly-owned U.S. Pat. No. 4,814,296 teaches cutting a slot in a back surface of a wafer with a blade and then cutting through the wafer from the front side with a blade. As shown in FIG. 7, the cut on the front side is aligned to be within a width of the back slot. To neutralize mechanical stresses, for example, cracking, due to the sawing process, U.S. Pat. No. 4,814,296 teaches the use of an additional step of etching the front surface to form a groove in which the front cut is made.
U.S. Pat. No. 7,498,238, teaches the use of a blade to partially notch a wafer and the use of a laser to generate reformed layers in a silicon cap portion added to the wafer to protect a construction on the wafer, for example, a sensor or a micro machine. The composite structure of the wafer and cap portion is stressed to generate cracks between the reformed layers to separate portions of the composite structure. The laser is not used to cut or generate reformed layers in the wafer itself.